The invention relates to a self-propelled harvesting machine comprising a front harvesting attachment and two drive shafts of a ground drive that are offset relative to the front harvesting attachment in the longitudinal direction of the harvesting machine. The drive shafts are drivably connected to track roller units that extend on both sides of the harvesting machine and run in the longitudinal direction thereof. A rear axle having rear wheels steered via a steering mechanism is provided in a rear region of the harvesting machine.
Working machines for earthwork usually comprise a ground drive designed as an endless track. The two track assemblies, which are designed as crawler drives, extend on both sides of the longitudinal mid-plane, substantially along the entire length of the chassis of the corresponding working machine. The traction means is designed as a steel chain in this case, wherein contact face elements are mounted on the steel chain by hinges and can be made of plastic or rubber, depending on the application of the working machine. The steel chain is disposed on drive sprockets and is supported in the region of the ground contact area thereof by support rollers. Chain arrangements are provided in which two drive sprockets are designed as deflection wheels and another drive sprocket functions as a drive wheel. In other chain arrangements, only two drive sprockets are provided, where each drive sprocket functions as a drive wheel and as a deflection wheel.
Designs of track assemblies also are known in which the chains provided with contact face elements are replaced by belt-drive track assemblies made of a rubber-metal composite material. In this case as well, the aforementioned support rollers are disposed between the two deflection wheels, which are guided on a frame, wherein the purpose of the support rollers, inter alia, is that of ensuring a more uniform load distribution and better adaptation to different ground contours.
In the past, such track assemblies were used on harvesting machines, in particular, when harvesting machines designed as self-propelled combine harvesters were used to harvest rice. Designing the ground drive as a crawler drive improves the cross-country mobility and the traction behavior of the harvesting machine equipped therewith, wherein the ground pressure also can be significantly reduced due to the larger ground contact area. These track assemblies also are finding increasing use on self-propelled harvesting machines are designed as combine harvesters or forage harvesters in particular, and which accommodate, in the front region thereof, a front attachment that can be raised and lowered.
Without appropriate crawler drives, fields to be harvested usually cannot be driven on after relatively long rainy periods and/or the harvesting machine sinks into the ground so far that the ground condition in the resultant tracks is markedly worsened. These track assemblies therefore also are used on combine harvesters that are used to harvest grain or rapeseed, or they are used on self-propelled forage harvesters for harvesting corn or grass silage so that harvesting can be carried out in a manner that protects the ground to the greatest possible extent, despite the fact that the ground is moist and, possibly, deeply tracked.
On the end thereof facing the front harvesting attachment, these harvesting machines are provided with a driven, non-steerable axle, while an axle on the rear-side end thereof, which is usually not driven, accommodates steerable wheels via spindles. A half-chain arrangement is provided, i.e., one of the drive axles (instead of the drive wheels) is provided with the track roller units, wherein these each typically have a profiled, endless belt band.
Self-propelled harvesting machines are operated on various ground conditions. For example, self-propelled harvesting machines travel on the field during a harvesting process as well as over relatively long stretches of asphalt-covered or paved roads on the approach to the field. An appropriate track roller unit, which is preferably provided with a belt band, has a substantial disadvantage in that, during maneuvering, extreme shear forces occur between the external profiling of the traction means and the ground. When traveling on an asphalt-covered road, the belt band undergoes increased wear during cornering or turning. On the field, the shear forces cause the ground to tear, which is also unwanted, since this alters and damages the ground structure. Some track assemblies are therefore provided with mechanisms for varying the ground contact area and, therefore, for improving the maneuverability of the harvesting machines such that the shear forces are reduced on the field and the turning radius is shortened when turning maneuvers are carried out.
A self-propelled harvesting machine provided with endless track assemblies is known from DE 41 93 720 T1. The endless track assembly described therein is a half-chain drive of a self-propelled combine harvester, in which the rear axle of the harvesting machine has steerable, non-driven wheels. Track assemblies having drive wheels (which are driven by a transmission via two drive shafts) and having deflection rollers and guide rollers are disposed in a first auxiliary frame that is fixedly connected to a main frame of the combine harvester. A second auxiliary frame, which is pivotably guided on the first auxiliary frame, accommodates the rear axle. Depending on a steer angle of the wheels of the rear axle, a so-called weight distribution cylinder is actuated such that, when steering lock occurs, the rear axle is displaced in the direction of the ground via the second auxiliary frame. As a result, a rear section of each of the track assemblies is lifted off the ground.
In addition, DE 10 2011 114 536 A1 discloses a combine harvester, which is equipped with track roller units and, in some of the exemplary embodiments, a rear axle having non-driven, steerable wheels. The track roller units in this case each comprise a belt band, a drive roller, two deflection rollers and support rollers. A ground contact area of each of the belt bands is intended to be reduced during road travel and when changing directions, i.e., when the wheels of the rear axle of the combine harvester are steered. For this purpose, the support rollers are displaced in the direction of the ground such that the deflection rollers lift off the ground and, therefore, the belt band has ground contact only in the region of the support rollers and a section located therebetween.
DE 40 16 496 A1 discloses a hydrostatic ground drive of a tracked vehicle, in which a hydraulic motor having an adjustable displacement volume is assigned to the drive of each of the track chains. The hydraulic motors are acted upon, via pressure medium lines, with different amounts of a pressure medium from one or more hydraulic pumps. In the document it is assumed that, in the case of crawler drives of construction machines, the ground drive is controlled such that the vehicle travels straight ahead when the transmission ratio of the two hydrostatic transmissions is the same and the vehicle travels around a curve when different amount of oil are fed to the hydraulic motors. The latter is intended to take place by means of a suitable adjustment of the delivery rates of the two hydraulic pumps.